Commissioning of the cosmic origins spectrograph on the Hubble Space Telescope: an overview of COS servicing mission observatory verification

The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R > 16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 A; and NUV, covering 1700 - 3200 A. Two low resolution gratings (R > 1500) cover the < 900 - 2050 A (FUV) and 1650 - 3200 A (NUV) wavelength regions. An imaging capability is also available on the NUV channel. As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout, fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this initial period was completed, science-related calibrations and verifications were performed in order to prepare the instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.